Diazepam is a sedative that is commonly used to facilitate examinations, as well as medical and surgical procedures on horses. It and its many metabolites are prohibited drugs for participation in many equine sports, including horse racing, FEI events and USEF competitions. It is helpful to know how long detection times persist in order for clients to enable appropriate withdrawal times and avoid positive tests for a prohibited substance.
A French study of six horses used an intravenous dose of 0.2 mg/kg of benzodiazepine diazepam (DIA), followed by collection of plasma samples until 16 days after dosing and urine samples 26 days after dosing. (Normal dosing of DIA in clinical practice ranges from 0.05 – 2.0 mg/kg depending on the desired effect of sedation or as an anti-convulsive.) [Schenk I, Machnik M, Broussou D, et al. Kinetic disposition of diazepam and its metabolites after intravenous administration of diazepam in the horse: Relevance for doping control. J Vet Pharmacol Therap May 2021; doi: 10.111/jvp.12991]
The detection time of 10 days—as stated by the European Horserace Scientific Liaison Committee—is the time for DIA plasma concentrations to drop below IPC.. To ensure safety from a positive drug test, the recommendation is that plasma of 90% of horses will fall below the IPC (irrelevant plasma concentration) 18 days after DIA administration. A note of caution: In the study, one horse had a detectable DIA metabolite in urine at 24 days.